The research involves analysis of the mechanism of action of the E. coli SecB protein in recognition of proteins destined to be exported out of the cell cytoplasm. Genetic studies will determine what features of the exported protein are recognized by SecB protein and what part of SecB protein is involved in the recognition. In addition, biochemical studies will determine the effects of secB mutations on protein translocation in vitro and characterize any interactions that might exist between SecB protein and polysomes that are translating exported proteins. For future research, these experiments will be extended to a detailed analysis of the interaction between SecB protein and its substrate. A second goal is to identify, through mutant isolation, other protein export factors that function like SecB protein but are specific for a different spectrum of exported proteins. Bacause secB mutations afect the export of only a subset of exported proteins, there is at lease one SecB-independent pathway for protein export. This pathway may include a factor that is functionally analogous to SecB protein. If this model is correct, the use of multiple pathways could provide the cell with a means with which to regulate the sites and rates of exort of different proteins. For orderly cell growth, the assembly of subcellular structures must be carefully controlled; the long term goal of this research is to understand the mechanism that allows the cell to perform this basic function.